1. Field of the Invention
The present invention relates to a method of operating a vacuum pump, and more particularly to a method of operating a vacuum pump for use in an evacuating system for a semiconductor fabrication apparatus.
2. Description of the Related Art
Vacuum pumps for use in evacuating systems for semiconductor fabrication apparatus generally do not have speed control means. Therefore, when such a vacuum pump starts to operate, it will subsequently continuously operate at a constant speed unless there is a reason to stop it. Even when an apparatus such as a semiconductor fabrication apparatus which is being evacuated by a vacuum pump stops its operation and no longer needs to be evacuated, the vacuum pump usually continues its operation. Reasons for continuously operating the vacuum pump even when it is not necessary to evacuate the semiconductor fabrication apparatus are as follows:
First, if the vacuum pump stopped, contaminants such as oil would flow back into the semiconductor fabrication apparatus that needs to be kept highly clean, and contaminate the semiconductor fabrication apparatus. Second, once the vacuum pump stopped, it would take a certain start-up time to operate the vacuum pump again for evacuating the semiconductor fabrication apparatus, resulting in a reduction in the throughput of the semiconductor fabrication apparatus. Third, various sublimated substances are generated in evaporation, sputtering, and CVD processes that are carried out by the semiconductor fabrication apparatus, and are constantly evacuated by the vacuum pump. If the vacuum pump stopped, those sublimated substances would be deposited in the vacuum pump and pipes connected thereto, possibly clogging the pipes or resulting in a failure to restart the vacuum pump.
For the above reasons, the conventional process of operating the vacuum pump suffers the following disadvantages:
Since the vacuum pump always operates at a constant speed, the vacuum pump wastes electric energy because it continues its operation even when the semiconductor fabrication apparatus does not need to be evacuated. Even during a time period when the semiconductor fabrication apparatus is vented to the atmosphere and does not need to be evacuated, it is not preferable to stop operating the vacuum pump only in such a time period.